Endocrine Abstracts

Annexin-1 (Anx-1), a 37kDa protein, is a member of the super-family of Ca²⁺- and phospholipid-binding annexin proteins and acts as a mediator of glucocorticoid (GC) action in the host defence and neuroendocrine systems. In the anterior pituitary Anx-1 is expressed mainly by folliculostellate (FS) cells and mediates the early delayed feedback inhibition exerted by GCs on the release of ACTH and other pituitary hormones.

The role of Anx-1 in the adrenal gland was investigated. It has already been shown that Anx-1 mRNA and protein is abundantly expressed in the adrenal gland. The localisation of Anx-1 was further investigated by in situ hybridisation, immunhistochemistry, electron microscopy and real-time PCR, using a cDNA tissue panel derived from perfused mouse adrenal tissues to eliminate contamination by Anx-1 expressing macrophages. The localisation of Anx-1 expression in the adrenal gland was also investigated by the localisation of x-gal reactivity in Anx-1 knock-out mice, which was shown to be in the peripheral part off the adrenal cortex. Functional studies were carried out using isolated primary adrenal cells in static cell culture incubations from both Anx-1 knock-out and wild-type mice. The cells from Anx-1 knock-out mice were found to be more responsive to ACTH stimulation compared to wild type controls. PCR studies indicate that there is no up-regulation of ACTH receptors in the adrenal gland of Anx-1 knock-out mice, therefore, these results are consistent with our hypothesis that Anx-1 may mediate a glucocorticoid ultra-short negative feedback loop in the adrenal gland. The effect of the potent Anx-1 2-26 peptide on steroid production is currently being investigated using perifused primary adrenal cells. In addition the responses of adrenal cells to ACTH in the presence and absence of the glucocorticoid receptor antagonist RU486 are being compared.